ST AN2048 Application note

AN2048

Application note

PD54008L-E: 8 W - 7 V LDMOS in PowerFLAT packages

for wireless meter reading applications

Introduction

STMicroelectronics has been strongly involved in finding new package solutions for power
integrated circuits to obta in a surface mount device (SMD). The PowerFLAT™ package
introduced in this application note shows the new concept of chip-size packaging
representing a fundamental step to reduce the costs of assembly and to shrink power
amplifier modules. This package helps maximize board space with improved electrical and
thermal performances over traditional packages with leads. This leadless package is an
MLP (micro leadframe pac kage) where th e electrical connect ions are mad e through landing
pads on the bottom surface of the component. These landing pads are soldered directly to
the pc board.

Figure 1. MLP cross section Figure 2. Intermodulation distortion versus

peak effective output power

The standard MLP has an exposed die attach pad which enhances the thermal and
electrical characteristics enabling high-power and high-frequency applications. For small
and medium-power applications, such as wireless PMR (private mobile radio) LDMOS
(Laterally Diffused MOS) transistors in PowerFLAT packages offer certain advantages
compared to equivalent bipolar transistors, for example, better intermodulation (IMD3).
Under certain conditions, an LDMOS transistor exhibits better intermodulation distortion
than a bipolar junction transistor. Figure 2 shows intermodulation distortion versus peak
effective o utput po wer f or eq uiv alently r ated bipola r and LDMOS tr ansistors . As w e can see ,
below 30 W, the LDMOS device has lower intermodulation distortion than the bipolar
transistor.

● Good gain linearity

● Smooth saturation

● Simpler bias circuit

● Thermal stability . The drain current has a positiv e temperature coefficient, theref ore the

MOS transistor is not susceptible to th ermal runaw ay.

● Better ruggedness

February 2008 Rev 2 1/13

www.st.com

Contents AN2048

Contents

1 Basic wireless meter reading system description . . . . . . . . . . . . . . . . . 4

2 Electrical requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

3 Circuit design and considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

3.1 Amplifier construction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

4 Circuit schematic and bill of material . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

5 Transmission line . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

5.1 Characterization results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

6 Components layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

7 Characterization results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

8 Feature characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

9 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

10 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

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AN2048 List of figures

List of figures

Figure 1. MLP cross section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Figure 2. Intermodulation distortion versus peak effective output power. . . . . . . . . . . . . . . . . . . . . . . 1

Figure 3. Network system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Figure 4. Source and load impedances of PD54008L-E . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Figure 5. Device footprint. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Figure 6. Cross section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Figure 7. Broadband power amplifier. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Figure 8. Transmission line . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Figure 9. Power gain vs. frequency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Figure 10. Input return loss vs. frequency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Figure 11. Drain efficiency vs. frequency. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Figure 12. Drain efficiency vs. frequency at different drain voltages . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Figure 13. Power out vs. drain voltage at different frequencies. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Figure 14. Impedance data schematic. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Figure 15. PCB layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Figure 16. PD54008L-E amplifier. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

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Basic wireless meter reading system description AN2048

1 Basic wireless meter reading system description

To reduce cost and difficulties associated with the reading of indoor utility meters for gas,
water and electricity, a new automatic meter reading system has rece ntly been introduced. It
uses radio frequency networks and allows direct data communication between reading
meters and services and/or the billing department. A DTU (Data Transmission Unit) module
that contains a powerful UHF narrow-band radio transmitter is attached to gas, water and
electric utility meters.

Figure 3. Network system

A DCU (Data Collector Unit) is placed in a convenient location within an apartment building
or housing complex.

The DCU contacts daily an NCC (Network Control Computer) and forwards the meter
reading information.

The NCC processes the information and provides billing data and customer support
information. This paper describes a DTU solution using an STMicroelectronics 8 W - 7 V
LDMOS device housed in a PowerFLAT and called PD54008L-E.

2 Electrical requirements

● V

● P

=5 V IDQ = 10 mA frequency band [450 ÷ 470] MHz

DD

= 36 dBm gain flatness < 1dB

out

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